To reproduce:
1) Open attached project and scene
2) Build and run for WebGL
3) Open it on chrome
4) Without moving mouse, scroll mouse wheel. You will see value changing
5) Move a mouse a bit - view only moves a bit like expected
6) Press Tab to hide and lock the cursor
7) Repeat steps 4-5 - this time the rotation randomly changes upon moving your mouse a bit. You might need to repeat this a few times, as some values don't make it change - but generally, most positive or negative (as long as the total didn't go deep into negatives) increments of 20+ were good enough to trigger this

Reproduced in Chrome 56.0.2924.87 (64-bit)
Not reproduced in Firefox 49.0

Reproduced in 5.3.6f1, 5.4.5f1, 5.5.2p2, 5.6.0b11, 2017.1.0a3